Advance directives permit competent adult patients to provide guidance regarding their care in the event that they lose the capacity to make medical decisions. One concern about the use of advance directives is the possibility that, in certain cases in which a patient undergoes massive psychological change, the individual who exists after such change is literally a (numerically) distinct individual from the person who completed the directive. If this is true, there is good reason to question the authority of the directive -- which is supposed to apply to the individual who completed it, not to someone else. This is 'the someone else problem'. After briefly introducing advance directives as a basis for medical decision-making, this paper elaborates 'the someone else problem' in the context of severe dementia. The paper then reconstructs the reasoning that leads to this putative problem and exposes the important underlying assumption that we are essentially persons. An alternative view of what we are, one that regards personhood as inessential, is then considered, before several arguments are advanced in favor of that alternative view. The paper next explores implications for advance directives: 'The someone else problem' is effectively dissolved, while it is noted that a related problem (one beyond the paper's scope) may persist. A few implications beyond advance directives are also identified.